The present invention relates to a method for treatment of drill cuttings to remove free hydrocarbons, including heavy crude oil and/or bitumen from the cuttings.
During the drilling of oil and/or gas wells, a drill bit at the end of a rotating drill string, or at the end of a drill motor, is used to penetrate through geologic formations. During this operation, drilling mud is circulated through the drill string, out of the bit, and returned to the surface via the annular space between the drill pipe and the formation. Among other functions, the drilling mud provides a washing action to remove the formation cuttings from the wellbore. The mud returns to the surface along with entrained drill cuttings and typically flows through xe2x80x9cshale shakers,xe2x80x9d desanders, desilters, hydrocyclones, centrifuges, and/or other known devices to separate the cuttings from the mud. The shale shaker(s), which typically sit above the mud storage area, essentially are screens that are used to separate the drill cuttings from the drilling mud. The drilling mud falls through the screens by gravity and the cuttings pass over the end of the screens.
The disposal of the drill cuttings after separation from the drilling mud can present a problem. One way to dispose of the cuttings would be to discharge the cuttings directly at the drilling site. An even more economically efficient way to dispose of drill cuttings would be to xe2x80x9crecyclexe2x80x9d the cuttings as components of building materials, such as concrete. Unfortunately, the cuttings may contain environmentally undesirable xe2x80x9cfree hydrocarbons,xe2x80x9d defined herein as hydrocarbons derived either from the drilling mud, from the rock formation, or both.
One approach that has been used to reduce potential environmental contamination by drill cuttings has been to minimize the toxicity of the oil-base fluids used to make drilling muds, and more recently, to use base fluids that are more biodegradable. Unfortunately, this approach does not eliminate contamination by the free hydrocarbons which originate in the rock formation rather than in the drilling fluid.
Methods are needed to treat cuttings, preferably in situ, to reduce the quantity of free hydrocarbons discharged into the environment upon subsequent use or disposal of the cuttings.
The invention provides a method comprising: providing cuttings produced during drilling operations comprising a first quantity of free hydrocarbons comprising bitumen; mixing with the cuttings a buffer solution comprising a buffer agent effective to activate at least one natural surfactant in the bitumen, thereby converting the solution into an emulsion comprising bitumen droplets having a mean average particle size of about 5 microns or less; and, thereafter adding to the emulsion an encapsulating material comprising an aqueous solution of a water soluble silicate under conditions effective to form silica shells around the droplets.